The 59-year-old suspect was detained two months after police announced a major forensic breakthrough in the unsolved investigation into the mass shooting at the village of Kingsmill, Co Armagh.

At the end of May, the Police Service of Northern Ireland (PSNI) revealed a potential match had been found to a palm print left on a getaway vehicle used by the republican paramilitaries.

The IRA was widely blamed for what was one of the most notorious outrages of the Troubles.

The factory workers were ambushed as they travelled along the Whitecross to Bessbrook road in rural south Armagh on January 5 1976 in an attack seen as a reprisal for loyalist killings in the same area.

The men's minibus was stopped by a man waving a red light and those on board were asked their religion by a camouflaged gunman with an English accent, whom the victims thought was a soldier.

The only Catholic workman was ordered to run away.

The killers, who had been hidden in the hedges, ordered the rest to line up outside the van and then opened fire.

The getaway vehicle used by the gunmen was left abandoned across the Irish border. The palm print was discovered later.

It was re-examined by forensic scientists only days after a long-delayed inquest into the deaths got under way in Belfast.

A lawyer for the PSNI told stunned relatives attending the hearing that a potential match on the police's database had been made.

One man survived the attack, despite being shot 18 times.

The suspect was arrested in Newry, Co Down on the suspicion of the ten murders and one attempted murder.